The hallmark of the aberrant cellular immune response in systemic lupus erythematosus (SLE) is T cell dysfunction (A. K. Dayal and G. M. Kammer, Arthritis Rheum. 39, 23 (1996); D. A. Horwitz, et al., in Dubois'Lupus Erythematosus., D. J. Wallace and B. H. Hahn, Eds. (Williams & Wilkins, Baltimore, 1997), chap. 10). An imbalance exists between exaggerated helper function and deficient cytotoxic/suppressor activity that promotes inappropriate B cell overproduction of immunoglobulins (Ig). The resulting polyclonal hypergammaglobulinemia is comprised of natural antibodies and pathogenic autoantibodies, including anti-native DNA. Formation of complement-fixing immune complexes in situ or their deposition on vascular endothelium, such as the renal glomerulus, initiates a chronic inflammatory response that leads to irreparable parenchymal damage, ultimately resulting in end-organ failure (R. P. Kimberly, in Arthritis and Allied Conditions: A Textbook of Rheumatology, W. J. Koopman, Ed. (Williams & Wilkins, Baltimore, 1997) chap. 27). Moreover, T cell dysfunctions predispose to recurrent, often life-threatening infections. See, A. G. Iliopoulos and G. C. Tsokos, Sem. Arthritis Rheum. 25, 318 (1996); C. A. Hunter and S. L. Reiner, Curr. Opin. Immunol. 12, 413 (2000).
Two principal defects of T cell function in SLE are augmented expression of cell surface receptors and altered production of cytokines. CD40 ligand (CD154) expression is significantly increased and prolonged on both CD4+ helper (Th) and CD8+ cytotoxic/suppressor (Tc) subpopulations (M. Koshy, et al., J. Clin. Invest. 98, 826 (1996); A. Desai-Mehta, et al, J. Clin. Invest. 97, 2063 (1996)). This prolonged over-expression may be pathophysiologically significant, for binding of CD154 on Th cells to CD40 on B cells promotes B cell activation and may drive the polyclonal hypergammaglobulinemia. Moreover, Th2 cells over-produce IL-10 whereas Th1 cells under-produce IFN-γ. Heightened levels of IL-10 may profoundly modify the cellular immune response by (a) downregulating both IFN-γ and IL-2 production by Th1 cells; (b) inhibiting IL-12 generation and down-regulating expression of IL-12 receptors on Th1 cells; (c) up-regulating bcl-2 expression and preventing apoptosis of activated T cells; and, (d) promoting B cell growth, differentiation and autoantibody production. By contrast, deficient IFN-γ may significantly hinder cellular immunity in SLE by both impairing Tc-dependent cytotoxicity and altering antigen-presentation (B. S. Handwerger, et al., in Lupus: Molecular and Cellular Pathogenesis, G. M. Kammer and G. C. Tsokos, Eds. (Humana Press, Totowa, N.J., 1999), chap. 21).
Histone deacetylases (HDACs) are enzymes that deacetylate specific lysine residues of histone amino-terminal tail domains and certain non-histone substrates. Current evidence implicates the deacetylases in transcriptional repression (T. Kouzarides, Curr. Opin. Genet. Dev. 9, 40 (1999); W. D. Cress and E. Seto, J. Cell. Physiol. 184, 1 (2000)). Complexed with Sin3 and Mi2 transcriptional co-repressor proteins, HDAC/Sin3 and HDAC/Mi2 associate with other DNA-binding proteins, such as Ikaros (W. D. Cress and E. Seto, J. Cell. Physiol. 184, 1 (2000); J. Kim et al., Immunity 10, 345 (1999)). These deacetylase complexes appear to limit the accessibility of transcription factors to the promoter by closely juxtaposing the nucleosome to DNA. Of the eight human HDACs discovered (W. D. Cress and E. Seto, J. Cell. Physiol. 184, 1 (2000)), to date only HDACs1-3 have been identified in T cells (F. Dangond et al., Biochem. Biophys. Res. Comm. 242, 648 (1998)). During T cell activation, HDAC/Mi2 complexes are recruited to regions of the heterochromatin by Ikaros and modulate gene expression (J. Kim et al., Immunity 10, 345 (1999); Koipally, J., et al. EMBO J 18, 3090 (1999)). Trichostatin A, an HDAC inhibitor (M. Yoshida, et al., J. Biol. Chem. 265, 17174 (1990); S. Finnin et al., Nature 401, 188 (1999)), blocks deacetylase activity and shifts the equilibrium toward histone acetylation. By acetylating histones, chromatin is remodeled, promoting access of DNA-binding transcription factors and the transcriptional machinery to promoter/enhancer regions (W. D. Cress and E. Seto, J. Cell. Physiol. 184, 1 (2000); R. D. Komberg and Y. Lorch, Curr. Opin. Gen. Dev. 9, 148 (1999)). Acetylation may mediate positive or negative regulatory events that depend upon the particular gene (Z. W. Sun and M. Hampsey, Genetics 152, 921 (1999)). Thus, promoter regions that are ordinarily silenced can then be derepressed whereas those that are expressed can be repressed. However, the use of histone deacetylase inhibitors or other histone hyperacetylating agents in the treatment of autoimmune diseases such as SLE has not heretofore been suggested or disclosed.
While several treatments for autoimmune diseases such as SLE and rheumatoid arthritis have been developed, none are entirely satisfactory. Hence, there remains a need for new ways to treat autoimmune diseases.